Should "The Choice" have a sad ending?

The choice is the story that i'm composição literária and it's about a teenager and her friends who have powers(oh, beware my overuse of the whole 'superpowers' thing. JK) and in the somewhat middle of the story, She finds out that she has to die in order to save the world. In the original plot, she lived, but I'm deciding to change it up a little bit, and I'm not sure whether or not to give the story a happy ending or a sad ending.
link - the fanpop spot.
link - the sneak peak that I put on deviantart.
I REALLY want some of your opinions.